JP2022118887A - Cold tool steel excellent in surface treatment characteristics and tool - Google Patents
Cold tool steel excellent in surface treatment characteristics and tool Download PDFInfo
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- 229910001315 Tool steel Inorganic materials 0.000 title abstract description 7
- 238000004381 surface treatment Methods 0.000 title abstract description 4
- 239000000463 material Substances 0.000 claims abstract description 31
- 229910000831 Steel Inorganic materials 0.000 claims abstract description 19
- 239000010959 steel Substances 0.000 claims abstract description 19
- 229910052758 niobium Inorganic materials 0.000 claims abstract description 7
- 229910052720 vanadium Inorganic materials 0.000 claims abstract description 7
- 229910052804 chromium Inorganic materials 0.000 claims abstract description 3
- 239000012535 impurity Substances 0.000 claims abstract description 3
- 229910052748 manganese Inorganic materials 0.000 claims abstract description 3
- 229910052750 molybdenum Inorganic materials 0.000 claims abstract description 3
- 229910052721 tungsten Inorganic materials 0.000 claims abstract description 3
- 239000010410 layer Substances 0.000 claims description 54
- 238000000576 coating method Methods 0.000 claims description 21
- 239000011248 coating agent Substances 0.000 claims description 20
- 229910000822 Cold-work tool steel Inorganic materials 0.000 claims description 19
- 239000002344 surface layer Substances 0.000 claims description 8
- 238000000034 method Methods 0.000 claims description 5
- 229910052742 iron Inorganic materials 0.000 abstract 1
- 238000005240 physical vapour deposition Methods 0.000 description 23
- 150000004767 nitrides Chemical class 0.000 description 15
- 238000005121 nitriding Methods 0.000 description 14
- 230000000694 effects Effects 0.000 description 9
- 238000012360 testing method Methods 0.000 description 7
- 238000011156 evaluation Methods 0.000 description 6
- 238000009863 impact test Methods 0.000 description 6
- 238000005496 tempering Methods 0.000 description 5
- 230000015572 biosynthetic process Effects 0.000 description 4
- 150000001247 metal acetylides Chemical class 0.000 description 4
- 239000000203 mixture Substances 0.000 description 4
- 238000010791 quenching Methods 0.000 description 4
- 230000000171 quenching effect Effects 0.000 description 4
- 239000000126 substance Substances 0.000 description 4
- 230000000052 comparative effect Effects 0.000 description 3
- 230000007423 decrease Effects 0.000 description 3
- 238000009826 distribution Methods 0.000 description 3
- 239000006104 solid solution Substances 0.000 description 3
- 239000000654 additive Substances 0.000 description 2
- 230000000996 additive effect Effects 0.000 description 2
- 238000005259 measurement Methods 0.000 description 2
- 238000005482 strain hardening Methods 0.000 description 2
- 239000000758 substrate Substances 0.000 description 2
- 229910000997 High-speed steel Inorganic materials 0.000 description 1
- 229910010037 TiAlN Inorganic materials 0.000 description 1
- 229910045601 alloy Inorganic materials 0.000 description 1
- 239000000956 alloy Substances 0.000 description 1
- 229910001566 austenite Inorganic materials 0.000 description 1
- 150000001875 compounds Chemical class 0.000 description 1
- 239000012141 concentrate Substances 0.000 description 1
- 239000000470 constituent Substances 0.000 description 1
- 230000000593 degrading effect Effects 0.000 description 1
- 230000002542 deteriorative effect Effects 0.000 description 1
- 238000011161 development Methods 0.000 description 1
- 229910003460 diamond Inorganic materials 0.000 description 1
- 239000010432 diamond Substances 0.000 description 1
- 238000005242 forging Methods 0.000 description 1
- 238000010438 heat treatment Methods 0.000 description 1
- 230000006698 induction Effects 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 239000011159 matrix material Substances 0.000 description 1
- 230000008018 melting Effects 0.000 description 1
- 238000002844 melting Methods 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 238000001556 precipitation Methods 0.000 description 1
- 238000012545 processing Methods 0.000 description 1
- 230000000717 retained effect Effects 0.000 description 1
- 229920006395 saturated elastomer Polymers 0.000 description 1
- 238000005204 segregation Methods 0.000 description 1
- 238000009628 steelmaking Methods 0.000 description 1
- 238000005728 strengthening Methods 0.000 description 1
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Abstract
Description
本発明は、冷間工具鋼と、この冷間工具鋼を基材に窒化とＰＶＤ法(物理気相蒸着法)による表面処理を施した金型及び工具に関する。 The present invention relates to a cold work tool steel, and a die and a tool obtained by subjecting the cold work tool steel to surface treatment by nitriding and PVD (Physical Vapor Deposition).
各種部材の軽量化や生産効率の向上を目的として、被加工材の高硬度化やニアネットシェイプ化が進展している。これに伴って、冷間金型および工具には、さらなる耐久力の向上が求められている。 In order to reduce the weight of various parts and improve production efficiency, work materials are being made to have higher hardness and near-net shape. Along with this, cold-work dies and tools are required to have further improved durability.
冷間工具鋼を基材とする金型にて飛躍的に耐久性を高める手法として、まず工具鋼に窒化を施して表面硬さを高め、さらにその上にＰＶＤにて硬質膜をコーティングさせる方法がある。
この際、窒化層の硬さが低いと、使用中に窒化層が変形しＰＶＤ処理膜が早期に剥離し、期待した耐久性が得られなくなる。
一方、窒化層が高硬度の場合も、窒化層内の硬度変化の勾配が急であると、窒化層と基材の工具鋼との境界に負荷が集中して剥離し、ＰＶＤ処理膜ごと欠落してしまい、期待する耐久性が得らなくなるという問題があった。
As a method for dramatically increasing the durability of molds that use cold work tool steel as a base material, the tool steel is first nitrided to increase its surface hardness, and then a PVD coating is applied on top of that to form a hard film. There is
At this time, if the hardness of the nitrided layer is low, the nitrided layer will be deformed during use and the PVD treated film will peel off early, making it impossible to obtain the expected durability.
On the other hand, even if the nitrided layer has a high hardness, if the gradient of the hardness change in the nitrided layer is steep, the load concentrates on the boundary between the nitrided layer and the tool steel of the base material, resulting in peeling and chipping of the entire PVD-treated film. As a result, there is a problem that the expected durability cannot be obtained.
出願人は、成分元素やその比率、そして結晶粒度を制御することによって、窒化の効果を有効に活用できる窒化処理に適したマトリクスハイス鋼を発明している（特許文献１参照。）。 The applicant has invented a matrix high-speed steel suitable for nitriding treatment in which the effect of nitriding can be effectively utilized by controlling the constituent elements, their ratios, and grain size (see Patent Document 1).
また、所定の成分の鋼を工具に成形し、その表面を窒化処理した後に、ＰＶＤ法又はＣＶＤ法による表面改質で形成した硬質被膜を形成する工具鋼が提案されている（特許文献２参照。）。この提案では硬質膜の密着性向上のためにＡｌが含有されている。 Further, a tool steel has been proposed in which a steel having a predetermined composition is formed into a tool, the surface of which is nitrided, and then a hard coating is formed by surface modification by PVD or CVD (see Patent Document 2). .). In this proposal, Al is contained in order to improve the adhesion of the hard film.
もっとも、前述の特許文献１では窒化層内の硬さ勾配までは考慮していない。また特許文献２も、窒化後の表面硬さや窒化深さ、また窒化層内の硬さ勾配については十分な考慮がなされておらず、ＰＶＤなどの硬質皮膜の剥離が生じる場合があった。 However, the aforementioned Patent Document 1 does not consider the hardness gradient in the nitride layer. Also, Patent Document 2 does not give sufficient consideration to the surface hardness after nitriding, the depth of nitriding, and the hardness gradient in the nitrided layer, so that peeling of hard coatings such as PVD may occur.
冷間加工用の金型では、ＰＶＤ処理膜の密着性を向上させるために、母材をプラズマ窒化処理して、母材の表面に化合物層のない窒化層を形成して硬化させたうえで、硬化被膜を付与することが有効と考えられる。
もっとも、窒化層の硬さが低いと、使用中に窒化層が変形し、ＰＶＤ処理膜が早期に剥離してしまう。一方、窒化層が高硬度であっても、窒化層内硬度変化が急だと、冷間加工時の応力で母材が変形したときに窒化層がその変形に追随できず、窒化層と母材の境界で剥離し、ＰＶＤ処理膜ごと欠落する場合があった。
In the mold for cold working, in order to improve the adhesion of the PVD-treated film, the base material is plasma-nitrided to form a nitrided layer without a compound layer on the surface of the base material, which is then hardened. , it is considered effective to apply a cured film.
However, if the hardness of the nitride layer is low, the nitride layer deforms during use, and the PVD-treated film peels off early. On the other hand, even if the nitrided layer has high hardness, if the hardness change in the nitrided layer is rapid, the nitrided layer cannot follow the deformation when the base material is deformed by the stress during cold working. In some cases, the material peeled off at the boundary of the material, and the entire PVD-treated film was missing.
そこで、本発明は、工具や金型表面に形成されたＰＶＤによる硬質皮膜と高い密着性を有して被膜の剥離を抑制する冷間工具鋼の提供、及びこの冷間工具鋼を母材に用いて表面にＰＶＤによる硬質皮膜が形成された金型や工具を提供することを目的としている。すなわち、靭性や耐剥離性といった表面処理特性に優れた冷間工具鋼の提供を目的とする。 Therefore, the present invention provides a cold work tool steel that has high adhesion to the PVD hard coating formed on the tool or mold surface and suppresses peeling of the coating, and this cold work tool steel is used as a base material. It is an object of the present invention to provide a mold or a tool having a surface formed with a hard coating by PVD using a hard coating. That is, the object is to provide a cold work tool steel excellent in surface treatment properties such as toughness and peeling resistance.
発明者らは鋭意開発を進めた結果、合金成分範囲、式、硬さ、さらに窒化した場合の表面硬さ、窒化層深さ、窒化層硬度変化を規定することで、ＰＶＤ処理等にて成膜した硬質膜と高い密着性を有する鋼および金型、工具が得られることを見出した。 As a result of diligent development, the inventors defined the alloy composition range, formula, hardness, surface hardness when nitrided, nitrided layer depth, and nitrided layer hardness change. It was found that a steel, a die and a tool having a hard film and high adhesiveness can be obtained.
すなわち、本発明の課題を解決するための第１の手段は、
質量％で、Ｃ：０．７～１．０％、Ｓｉ：０．３～１．０％、Ｍｎ：０．５％以下、Ｃｒ：３．５～９．０％、Ｍｏ：１．５～６．０％、Ｗ：８．０％以下、Ｖ及びＮｂ：Ｖ＋Ｎｂ／２で０．２～２．０％、Ｎ：５００ｐｐｍ未満、残部Ｆｅ及び不可避的不純物からなり、式ＳのＳ値が３５以上、式ＩのＩ値が１５０以上の鋼を、さらに焼入焼戻しされた状態で鋼材硬さが５８ＨＲＣ以上である、冷間工具鋼。
式Ｓ：Ｓ＝２．０Ｃｒ＋１４．０Ｍｏ＋３．３Ｗ＋６．７（Ｖ＋Ｎｂ／２）
式Ｉ：Ｉ＝７０Ｓｉ－Ｃｒ＋６３Ｍｏ－１５３Ｖ＋２３Ｗ
但し、式の元素記号には当該成分の％値を代入する。
That is, the first means for solving the problems of the present invention is
% by mass, C: 0.7 to 1.0%, Si: 0.3 to 1.0%, Mn: 0.5% or less, Cr: 3.5 to 9.0%, Mo: 1.5 ~ 6.0%, W: 8.0% or less, V and Nb: 0.2 to 2.0% at V + Nb / 2, N: less than 500 ppm, balance Fe and unavoidable impurities, S value of formula S is 35 or more, the I value of formula I is 150 or more, and the steel hardness in the quenched and tempered state is 58 HRC or more.
Formula S: S=2.0Cr+14.0Mo+3.3W+6.7(V+Nb/2)
Formula I: I=70Si-Cr+63Mo-153V+23W
However, the % value of the component concerned is substituted for the symbol of the element in the formula.
その第２の手段は、第１の手段に記載の冷間工具鋼に、さらに窒化層が表層に形成されたものであって、窒化層の最表面から３０μｍの深さでの硬さが８００ＨＶ以上、その窒化層深さが６０μｍ以上、窒化層の最表面から３０μｍ位置と６０μｍ位置とでの硬度変化が７５ＨＶ以内である、窒化層を備えた冷間工具鋼である。 The second means is the cold work tool steel described in the first means, in which a nitride layer is further formed on the surface layer, and the hardness at a depth of 30 μm from the outermost surface of the nitride layer is 800 HV. As described above, the cold work tool steel provided with a nitrided layer has a nitrided layer depth of 60 μm or more and a hardness change of 75 HV or less between positions 30 μm and 60 μm from the outermost surface of the nitrided layer.
その第３の手段は、第１又は第２の手段の冷間工具鋼を母材として、表層にさらにＰＶＤ法で形成された硬質被膜を備える金型である。 The third means is a mold that uses the cold work tool steel of the first or second means as a base material and further has a hard coating formed on the surface layer by a PVD method.
その第４の手段は、第１又は第２の手段の冷間工具鋼を母材として、表層にさらにＰＶＤ法で形成された硬質被膜を備える工具である。 The fourth means is a tool comprising the cold work tool steel of the first or second means as a base material and further having a hard coating formed on the surface layer by a PVD method.
本発明の冷間工具鋼を母材とすると、冷間工具鋼としての靭性と硬さといった母材の特性を備え、さらに表層にＰＶＤによる硬質被膜を形成すると、表面硬さが確保され、また表面での急激な硬度変化が抑制されるので、ＰＶＤ硬質皮膜の剥離や欠落が抑制されることとなる。母材表層に窒化層を形成したうえに、ＰＶＤ硬質被膜を形成させた金型や工具は、硬質被膜との密着性に優れ、急激な硬度変化も抑制され、剥離や欠落がより抑制されることとなる。すなわち、本発明の冷間工具鋼を母材として表層にＰＶＤの硬質被膜を形成させたものは、シャルピー衝撃試験でシャルピー衝撃値が２０Ｊ／ｃｍ2以上で、スクラッチ試験による剥離臨界荷重も８０Ｎ以上であるから、靭性、耐剥離性のいずれにも優れるものとなる。 When the cold work tool steel of the present invention is used as a base material, it has the characteristics of the base material such as toughness and hardness as a cold work tool steel, and when a hard coating is formed on the surface layer by PVD, the surface hardness is ensured. Since rapid changes in hardness on the surface are suppressed, peeling and chipping of the PVD hard coating are suppressed. Dies and tools with a nitride layer formed on the surface of the base material and a PVD hard coating have excellent adhesion to the hard coating, suppress rapid changes in hardness, and further suppress peeling and chipping. It will happen. That is, when the cold work tool steel of the present invention is used as a base material and a PVD hard coating is formed on the surface layer, the Charpy impact value in the Charpy impact test is 20 J/cm 2 or more, and the peeling critical load in the scratch test is 80 N or more. Therefore, it is excellent in both toughness and peeling resistance.
本発明を実施するための形態の説明に先立って、本願の手段における鋼の化学成分を規定する理由、式Ｓ及び式Ｉの値を規定する理由、焼入焼戻し後の鋼材硬さ、窒化層の硬さ、窒化層の硬度変化を規定する理由について説明する。
なお、以下の化学成分における％は質量％である。
Prior to the description of the mode for carrying out the present invention, the reasons for specifying the chemical composition of the steel in the means of the present application, the reasons for specifying the values of formula S and formula I, the hardness of the steel material after quenching and tempering, and the nitride layer The reason for specifying the hardness of the nitride layer and the hardness change of the nitride layer will be explained.
In addition, % in the following chemical components is mass %.
Ｃ：０．７～１．０％
Ｃは、鋼中への固溶および炭化物形成にて工具鋼に必要な高硬度を付与させるのに必須の元素である。工具としての硬度を得るためには、少なくともＣは０．７％は必要である。もっとも、Ｃが１．０％を超えると、粗大炭化物を多く形成し易くなり、鋼材自体の靭性と基材と膜との密着性を低下させる。そこで、Ｃは０．７～１．０％、好ましくは、Ｃは０．７～０．９％である。
C: 0.7-1.0%
C is an essential element for imparting the necessary high hardness to the tool steel through solid solution and carbide formation in the steel. At least 0.7% of C is required to obtain hardness as a tool. However, if C exceeds 1.0%, a large amount of coarse carbides is likely to be formed, which lowers the toughness of the steel material itself and the adhesion between the substrate and the film. Therefore, C is 0.7-1.0%, preferably C is 0.7-0.9%.
Ｓｉ：０．３～１．０％
Ｓｉは製鋼での脱酸効果、焼入性、固溶強化に寄与する。そのためには少なくともＳｉは０．３％以上必要である。もっとも、Ｓｉが１．０％を超えると靭性が低下する。そこで、Ｓｉは０．３～１．０％とする。好ましくは、Ｓｉは０．４～１．０％である。
Si: 0.3-1.0%
Si contributes to the deoxidizing effect, hardenability, and solid-solution strengthening in steelmaking. For that purpose, at least 0.3% or more of Si is required. However, when Si exceeds 1.0%, the toughness decreases. Therefore, Si should be 0.3 to 1.0%. Preferably, Si is 0.4-1.0%.
Ｍｎ：０．５％以下
Ｍｎは、０．５％を超えると残留オーステナイトの増大や偏析帯の形成を促して靭性、変寸異方性を悪化させる。そこで、Ｍｎは０．５％以下とする。
Mn: 0.5% or less When Mn exceeds 0.5%, it promotes an increase in retained austenite and the formation of segregation bands, thereby deteriorating toughness and dimensional anisotropy. Therefore, Mn should be 0.5% or less.
Ｃｒ：３．５～９．０％
Ｃｒは、焼入性の向上と焼戻硬さの確保に必要な元素である。もっとも、Ｃｒが３．５％未満ではこれらの効果が不十分である。他方、Ｃｒが９．０％を超えると、粗大炭化物を多く形成し易くなり、鋼材自体の靭性と基材と膜との密着性を低下させる。そこで、Ｃｒは３．５～９．０％とする。好ましくはＣｒは４．５～８．５％である。
Cr: 3.5-9.0%
Cr is an element necessary for improving hardenability and securing temper hardness. However, if Cr is less than 3.5%, these effects are insufficient. On the other hand, when Cr exceeds 9.0%, a large amount of coarse carbides is likely to be formed, degrading the toughness of the steel material itself and the adhesion between the substrate and the film. Therefore, Cr should be 3.5 to 9.0%. Cr is preferably 4.5 to 8.5%.
Ｍｏ：１．５～６．０％
Ｍｏは、焼入性改善と、焼戻硬さ向上に寄与する。その効果を得る為にはＭｏは少なくとも１．５％は必要である。他方、Ｍｏが６．０％を超えると、これらの効果は飽和し、過剰添加は粗大炭化物の形成を促して膜との密着性を低下させる。そこでＭｏは１．５～６．０％とする。好ましくは、Ｍｏは１．５～５．０％である。
Mo: 1.5-6.0%
Mo contributes to improvement of hardenability and temper hardness. At least 1.5% of Mo is required to obtain the effect. On the other hand, when Mo exceeds 6.0%, these effects are saturated, and excessive addition promotes the formation of coarse carbides and reduces adhesion to the film. Therefore, Mo is set to 1.5 to 6.0%. Preferably, Mo is 1.5-5.0%.
Ｗ：８．０％以下
ＷはＭｏと似た効果を持つが、８．０％を超えるとＭｏ同様、逆効果となる。そこで、Ｗは８．０％以下とする。
W: 8.0% or less W has an effect similar to that of Mo, but if it exceeds 8.0%, it has the opposite effect like Mo. Therefore, W is set to 8.0% or less.
Ｖ＋Ｎｂ／２：０．２～２．０％
Ｖ及びＮｂは、いずれも焼戻し時に微細かつ硬質な析出硬化物を形成し二次硬化に寄与する。それらの効果を得る為には、ＶとＮｂの合計量で、少なくともＶ＋Ｎｂ／２が０．２％以上であることが必要である。もっとも、Ｖ＋Ｎｂ／２が２．０％を超えると、Ｖ及びＮｂが過剰となって粗大炭化物の形成を促し、膜との密着性の低下を招く。
そこで、Ｖ及びＮｂは、Ｖ＋Ｎｂ／２で０．２～２．０％とする。好ましくはＶ＋Ｎｂ／２が０．２～１．８％である。
V+Nb/2: 0.2 to 2.0%
Both V and Nb form fine and hard precipitation hardened substances during tempering and contribute to secondary hardening. In order to obtain these effects, the total amount of V and Nb should be at least V+Nb/2 of 0.2% or more. However, if V+Nb/2 exceeds 2.0%, V and Nb become excessive and promote the formation of coarse carbides, resulting in a decrease in adhesion to the film.
Therefore, V and Nb are set to 0.2 to 2.0% as V+Nb/2. V+Nb/2 is preferably 0.2 to 1.8%.
Ｎ：５００ｐｐｍ以下
ＮはＣと似た効果を持つが、５００ｐｐｍを超えると、硬質で固溶し難い窒化物を形成して鋼材の靭性を著しく低下させる。そこでＮは５００ｐｐｍ以下とする。好ましくはＮは４００ｐｐｍ以下である。
N: 500 ppm or less N has an effect similar to that of C, but if it exceeds 500 ppm, it forms hard nitrides that are difficult to form a solid solution, and significantly lowers the toughness of the steel material. Therefore, N is set to 500 ppm or less. Preferably N is 400 ppm or less.
Ｓ＝２．０Ｃｒ＋１４．０Ｍｏ＋３．３Ｗ＋６．７（Ｖ＋Ｎｂ／２）≧３５
式Ｓの値Ｓは、各添加元素の種類と量（式の元素記号には％の値を代入する。）から窒化処理後の表面硬さ予測する指標である。Ｓの値が大きい程、表面硬さも大きくなる。Ｓが３５より小さいと、表面硬さが不足して密着性が低下する。そこで、Ｓの値は３５以上とする。
S=2.0Cr+14.0Mo+3.3W+6.7(V+Nb/2)≧35
The value S of the formula S is an index for predicting the surface hardness after nitriding from the type and amount of each additive element (substitute the value of % for the symbol of the element in the formula). The higher the value of S, the higher the surface hardness. When S is less than 35, the surface hardness is insufficient and the adhesion is lowered. Therefore, the value of S is set to 35 or more.
Ｉ＝７０Ｓｉ－１Ｃｒ＋６３Ｍｏ－１５３Ｖ＋２３Ｗ≧１５０
式Ｉの値Ｉは、各添加元素の種類と量（式の元素記号には％の値を代入する。）から窒化層内の硬さ分布を予測する指標である。Ｉの値が大きい程、窒化層内の硬度変化は小さくなる。Ｉの値が１５０より小さいと、膜の剥離や欠落が生じやすくなる。そこで、Ｉの値は１５０以上とする。
I=70Si-1Cr+63Mo-153V+23W≧150
The value I in Formula I is an index for predicting the hardness distribution in the nitrided layer from the type and amount of each additive element (the value of % is substituted for the symbol of the element in the formula). The higher the value of I, the smaller the hardness variation in the nitrided layer. If the value of I is less than 150, peeling or chipping of the film is likely to occur. Therefore, the value of I is set to 150 or more.
焼入焼戻し後の鋼材硬さ：５８ＨＲＣ以上
焼入焼戻ししたときの硬さが５８ＨＲＣを下回ると、硬質被膜との密着性が悪化することから、母材の鋼材硬さは、５８ＨＲＣ以上とする。
Steel hardness after quenching and tempering: 58 HRC or more If the hardness after quenching and tempering is less than 58 HRC, the adhesion with the hard coating deteriorates.
母材表層の窒化処理後の表面硬さ：窒化層の最表面から深さ３０μｍの位置で８００ＨＶ以上
母材となる本発明の冷間工具鋼を窒化処理したとき、その表面（最表面から深さ３０μｍの位置）の硬さを８００ＨＶ以上とすると、ＰＶＤ硬質皮膜及び母材との密着性が特に向上する。そこで、窒化層の最表面から深さ３０μｍの位置の表面硬さを８００ＨＶ以上とする。
なお、窒化処理はプラズマ窒化処理が好適である。以下の説明ではプラズマ窒化処理を例に説明する。
Surface hardness after nitriding treatment of base material surface layer: 800 HV or more at a position 30 μm deep from the outermost surface of the nitrided layer When the cold work tool steel of the present invention, which is the base material, is nitrided, When the hardness at the position of 30 μm in height) is 800 HV or more, the adhesion between the PVD hard coating and the base material is particularly improved. Therefore, the surface hardness of the nitride layer at a depth of 30 μm from the outermost surface is set to 800 HV or more.
Plasma nitriding is suitable for the nitriding. In the following explanation, the plasma nitriding treatment will be explained as an example.
窒化処理後の窒化層の深さ：６０μｍ以上
プラズマ窒化処理で形成される窒化層は、その窒化層深さが６０μｍより小さくなると、ＰＶＤ硬質皮膜及び母材との密着性が低下する。このため、窒化層深さは６０μｍ以上とした。
Depth of Nitrided Layer after Nitriding Treatment: 60 μm or More When the depth of the nitrided layer formed by plasma nitriding treatment is less than 60 μm, the adhesion between the PVD hard coating and the base material decreases. Therefore, the depth of the nitride layer is set to 60 μm or more.
窒化層の硬度変化：７５ＨＶ以内
窒化層の最表面から深さ３０μｍ位置と深さ６０μｍ位置での硬度変化の度合いが７５ＨＶより大きくなると、膜直下と内部で硬度差が大きくなっているため剥離を助長してしまい、母材との密着性が低下する。そこで、上記の硬度変化は７５ＨＶ以下とした。
Nitrided layer hardness change: within 75 HV If the degree of hardness change at a depth of 30 μm and a depth of 60 μm from the top surface of the nitrided layer is greater than 75 HV, peeling will occur due to the large difference in hardness between directly under the film and inside. The adhesion to the base material deteriorates. Therefore, the above hardness change is set to 75 HV or less.
（実施例について）
まず、表１に示す化学成分と残部Ｆｅからなる鋼１００ｋｇを真空誘導溶解炉にて溶製し、各々鍛伸温度１１００～１２００℃で角３０ｍｍに鍛伸後切断、焼入焼戻し処理を行った。
その後、ロックウェル硬度計にて角材断面中周部の鋼材硬さを測定した。次いで、角材長手方向と平行にシャルピー衝撃試験片（１０Ｒ－Ｃノッチ）を作製し、シャルピー衝撃試験にて靭性を評価した。
(About Examples)
First, 100 kg of steel composed of the chemical composition shown in Table 1 and the balance Fe was melted in a vacuum induction melting furnace, and each was forged and stretched to a square of 30 mm at a forging temperature of 1100 to 1200 ° C., cut, and quenched and tempered. .
After that, the hardness of the steel material at the central portion of the cross section of the square bar was measured with a Rockwell hardness tester. Next, a Charpy impact test piece (10R-C notch) was prepared parallel to the longitudinal direction of the square bar, and the toughness was evaluated by the Charpy impact test.
（評価Ｉ）
シャルピー衝撃試験値が２０Ｊ／ｃｍ2以上のものを靭性に優れるとして○、それ未満のものを靭性に劣るとして×と評価した。
(Evaluation I)
A sample with a Charpy impact test value of 20 J/cm 2 or more was evaluated as excellent in toughness, and a sample with a Charpy impact test value of less than 20 J/cm 2 was rated as poor in toughness.
評価Ｉの後、各鋼材について、焼入焼戻し後の角３０ｍｍ材から幅２５×厚さ７ｍｍ×長さ５０ｍｍ小片を割出し、その表面にプラズマ窒化処理（５００℃加熱）を行って窒化膜層を形成した後、さらに窒化膜層の上にＰＶＤ処理にてＴｉＡｌＮを成膜した。 After evaluation I, for each steel material, a 25 mm wide x 7 mm thick x 50 mm long small piece was indexed from the 30 mm square material after quenching and tempering, and plasma nitriding treatment (heating at 500 ° C.) was performed on the surface to form a nitride film layer. was formed, a TiAlN film was further formed on the nitride film layer by PVD processing.
ＰＶＤ処理後の小片から長さ５ｍｍ程度切出し、その切断面にて窒化層深さと窒化層の硬度変化を計測した。 A piece of about 5 mm in length was cut from the small piece after the PVD treatment, and the depth of the nitrided layer and the change in hardness of the nitrided layer were measured on the cut surface.
（窒化層深さの測定について）
マイクロビッカース硬度計にて切断面の被膜直下、つまり窒化層再表面から深さ３０μｍの位置を始点とし、深さ２００μｍまで１０μｍピッチで窒化層内の硬さ分布を測定した。
(Measurement of nitride layer depth)
Using a micro Vickers hardness meter, the hardness distribution in the nitrided layer was measured at a pitch of 10 μm up to a depth of 200 μm starting from a position immediately below the film on the cut surface, that is, at a depth of 30 μm from the surface of the nitrided layer.
また、窒化層再表面から深さ１１００μｍ位置を始点とし、深さ２０００μｍまで１００μｍピッチで硬さを測定して、その１０点の硬さの平均値を「内部ビッカース硬さ」とした。 Further, the hardness was measured at a pitch of 100 μm to a depth of 2000 μm from a position of 1100 μm deep from the surface of the nitrided layer as a starting point, and the average value of hardness at 10 points was defined as “internal Vickers hardness”.
窒化層深さは、１０μｍピッチで測定した窒化層内３０～２００μｍの硬さ分布において、上記内部ビッカース硬さよりも２５ポイント以上高い値を示す位置の中で最も深い位置を「窒化層深さ」とした。 The nitrided layer depth is the deepest position among the positions showing a value higher than the internal Vickers hardness by 25 points or more in the hardness distribution of 30 to 200 μm in the nitrided layer measured at a pitch of 10 μm. and
（窒化層の硬度変化）
上記窒化層深さの際に測定した、マイクロビッカース硬度計による窒化層最表面から深さ３０μｍおよび６０μｍ位置の硬さの差を硬度差とした。
(Change in hardness of nitrided layer)
The difference in hardness at positions of 30 μm and 60 μm in depth from the outermost surface of the nitrided layer measured with a micro Vickers hardness tester at the time of determining the depth of the nitrided layer was taken as the difference in hardness.
（スクラッチ試験による剥離臨界荷重の計測）
評価Ｉにて○の評価となったもの、すなわち十分な靭性が得られたものについてのみ、さらに幅２５×厚さ７ｍｍ×長さ５０ｍｍ小片の残材を使用して、スクラッチ試験による剥離臨界荷重を計測した。したがって、比較鋼Ｎｏ．１９～３１については、靭性がなく、そもそも冷間工具鋼としての特性を備えていないため、スクラッチ試験は実施していない。
(Measurement of peeling critical load by scratch test)
Only those that were evaluated as ○ in Evaluation I, that is, those that had sufficient toughness, were further subjected to a peeling critical load by a scratch test using a remaining piece of width 25 × thickness 7 mm × length 50 mm. was measured. Therefore, comparative steel No. No scratch test was conducted for Nos. 19 to 31 because they lacked toughness and inherently did not have the characteristics of cold work tool steel.
試験条件は、最小荷重：１Ｎ、荷重スピード：３０Ｎ／ｍｉｎ、スクラッチスピード：１．５１ｍｍ／ｍｉｎ、圧子：ダイアモンド、圧子曲率半径：２００μｍとした。 The test conditions were as follows: minimum load: 1 N, load speed: 30 N/min, scratch speed: 1.51 mm/min, indenter: diamond, and indenter curvature radius: 200 μm.
（評価ＩＩ）
スクラッチ試験による剥離臨界荷重が１００Ｎ以上のものを耐剥離性に優れるものとして○、８０以上のものを可として△に、それ未満のものを耐剥離性不良として×と評価した。
(Evaluation II)
Those with a peeling critical load of 100 N or more in the scratch test were evaluated as excellent in peel resistance, those with 80 or more were evaluated as acceptable, and those below that were evaluated as poor in peel resistance.
表２にシャルピー衝撃試験の評価Ｉとスクラッチ試験の評価ＩＩの結果をに示す。 Table 2 shows the results of evaluation I of the Charpy impact test and evaluation II of the scratch test.
発明鋼Ｎｏ．１～１８は、プラズマ窒化処理により形成された窒化層の上に、さらに形成されたＰＶＤ硬質被膜が付与されることで、靭性に優れる一方、硬質皮膜が母材から剥離しにくいものとなっていることが確認された。 Invention Steel No. In Nos. 1 to 18, a PVD hard coating is further formed on the nitrided layer formed by plasma nitriding treatment, resulting in excellent toughness and hard coating peeling off from the base material. It was confirmed that
比較鋼Ｎｏ．１９～３１は、シャルピー衝撃値が２０Ｊ／ｃｍ2未満であり、靭性に劣るものとなった。比較鋼Ｎｏ．３２～３４は、剥離臨界荷重が７４Ｎ以下であり、８０Ｎを下回ったので、耐剥離性に劣る結果となった。 Comparative steel no. 19 to 31 had a Charpy impact value of less than 20 J/cm 2 and were inferior in toughness. Comparative steel no. In Nos. 32 to 34, the peeling critical load was 74 N or less, which was lower than 80 N, resulting in inferior peeling resistance.
Claims (4)
式Ｓ：Ｓ＝２．０Ｃｒ＋１４．０Ｍｏ＋３．３Ｗ＋６．７（Ｖ＋Ｎｂ／２）
式Ｉ：Ｉ＝７０Ｓｉ－Ｃｒ＋６３Ｍｏ－１５３Ｖ＋２３Ｗ
但し、式の元素記号には当該成分の％値を代入する。 % by mass, C: 0.7 to 1.0%, Si: 0.3 to 1.0%, Mn: 0.5% or less, Cr: 3.5 to 9.0%, Mo: 1.5 ~ 6.0%, W: 8.0% or less, V and Nb: 0.2 to 2.0% at V + Nb / 2, N: less than 500 ppm, balance Fe and unavoidable impurities, S value of formula S is 35 or more, the I value of formula I is 150 or more, and the steel hardness in the quenched and tempered state is 58 HRC or more.
Formula S: S=2.0Cr+14.0Mo+3.3W+6.7(V+Nb/2)
Formula I: I=70Si-Cr+63Mo-153V+23W
However, the % value of the component concerned is substituted for the symbol of the element in the formula.
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